An iPhone requests the user’s password upon restart, this would be referred to as “first unlock”. The reward is for an exploit that takes place against a _locked device_ but only after it has been unlocked once first. As in, an exploit that applies to the Lock Screen when the device was previously unlocked at least once. It is likely easier to trick a locked system into unlocking after it has already been unlocked the first time, due to password storage, credentialed background processes, and so on.